IRSN and public protection against exposure to low dosesof ionizing radiation
IRSN FACT SHEETS

June 2021

www.irsn.fr

What is a dose of ionizing radiation?
Some examples ofhuman exposure sources(expressed in effective dose)

When ionizing radiation penetrates living material, it transfers a certain amount of energy to it, known as the "dose” andexpressed as a unit called gray (Gy), which is equivalent to one joule per kilogram of material.
When radiation is absorbed by an organism, biological effects can be observed; they differ according to the type of radiation(alpha, beta, gamma, neutron, etc.) and the irradiated tissue or organ (bone marrow, colon, lung, breast, etc.). The sum of
the doses over all organs is the “effective dose”. This is expressed in sievert (Sv), a unit that reports the degree ofharmfulness specific to each type of radiation and the radiosensitivity of each tissue or organ.
Ionizing radiation can have a direct influence on DNA, disrupting cell reproduction. It can also damage essential cellular
structures, sometimes leading to the onset of diseases, such as cancer.
Two types of effects are observed, depending on the absorbed dose:•at high doses, specific short-term radiation effects (from a few days to a few months after exposure), such asradiation-induced burns, hair loss, changes in blood count levels, etc.;•

at low to moderate doses, non-specific ionizing radiation effects, which may occur randomly in the longer term
(between a few years or decades after exposure), such as cancer, cardiovascular disease, or eye lens opacity .

The notion of low doses: an evolving concept
The notion of “low doses” is far from fixed. It has evolved as knowledge on the effects of exposure to ionizing radiation on
the body has advanced. Over time, the levels considered as “low doses” have steadily decreased.
Today, one of the most commonly accepted definitions is the one given by the United Nations Scientific Committee on theEffects of Ionizing Radiation (UNSCEAR), which considers cumulative doses below 100 mGy as “low”.

Concepts subject to interpretation
The concept of “low doses” is not only evolving, but is also understood differently according to points of view (scientists,healthcare workers, industry, politicians, etc.). Within the scientific community itself, its acceptance varies according to thedisciplines concerned (biologists, epidemiologists, ecotoxicologists, radiotoxicologists, etc.).
A second controversial concept is the “linear no-threshold model” which expresses the proportionality between the doses
received and the health risk. This extrapolation, based on the effects observed at high doses, used by international
committees to allow simple management of radiological risks, is discussed on the basis of the observation of biologicalmechanisms that are non-linear with dose. Nevertheless, today, epidemiological results on cancer still argue in favor ofusing the simple linear model for radiation protection.
Furthermore, the existence or not of non-cancer effects at low doses, particularly on the cardiovascular system and the eyelens, is also debated. Determination of the effect of co-exposure to multiple stressors (radiological, chemical, etc.), forexample, the combined effect of radon and tobacco in the onset of lung cancer, is complex and still poorly characterized.

Contribution of epidemiological studies on various cohorts
Prior to the 1990s, knowledge on health risks due to ionizing radiation was mainly based on the results of epidemiologicalfollow-up of survivors of the Hiroshima and Nagasaki bombings, as well as that of patients treated with radiotherapy.

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From the 1990s onwards, epidemiological studies considered other populations, such as medical staff, patients undergoing
diagnosis examinations, nuclear workers, and the general population. Today, the some 30 years of follow-up of thesecohorts have improved our knowledge of radiation-induced risks, taking into account daily exposure situations and thespecific nature of the different populations (European, American, Asian, etc.). The statistical power of these studies has
increased significantly, enabling meaningful scientific results to be obtained for exposures below 100 mSv.
An worldwide dynamic has begun with studies published over the past two years by major international stakeholders –such as the U.S. National Council for Radiation Protection and Dosimetry (NCRP), the International Commission on
Radiological Protection (ICRP), and the U.S. National Cancer Institute (NCI) – which confirm the concordance of effects
observed at low doses.

Some key lessons learned about low doses
IRSN is a French Stateowned industrial andcommercial establishment(EPIC) the missions, status,and operation of which aredetermined by Articles L59245 to L592-49 and R592-39
to R592-61 of the French
Environment Code. IRSN isunder the joint supervision ofthe French Minister for theEnvironment, the French theMinister of Defense, and theFrench Ministers of Energy,
Research, and Health.
As a public expert, IRSN
advances scientificknowledge to manage all
nuclear and radiation risks.
Through its research,
methods, and interactions
with all stakeholders, IRSN
assesses these risks andtheir consequencesindependently. It thus
contributes to theirprevention, detection, andthe limitation of their
possible effects, in order toprotect the population andthe environment.

Radiobiology studies first showed that there was no single form of dose-response relationship for all cellular biologicalprocesses. They also demonstrated that exposure to ionizing radiation can have indirect effects on other cellularconstituents, such as water molecules, in addition to direct effects on DNA, which may also play a role in thedevelopment of diseases induced by exposure to ionizing radiation.
Another lesson is that individual characteristics (age, sex, genetic predisposition, etc.) can modulate the risk ofdeveloping cancer. The impact of these individual sensitivities to exposure to ionizing radiation is currently underdebate.

IRSN’s contribution to international research on low doses
The Institute participated in the structuring of European research in this area with the creation, in 2009, of MELODI(Multidisciplinary European Low Dose Initiative), a structure for the governance of research on low doses, and, in 2010,of the DoReMi (Low dose research towards multidisciplinary integration) network of excellence, followed by the OPERRA(2013) and CONCERT (2017) programs financed by the European Commission.
IRSN also participates in or leads international studies on different exposure situations:•natural exposure to radon: IRSN has conducted several years of studies on uranium miners and the effect ofdomestic exposure to radon. The results obtained helped demonstrate the risk of lung cancer associated withradon, even at low exposure levels. Today, the Institute is working on the European RadoNorm project;•post-accident exposure: after conducting the EPICE study on the health consequences of the Chernobyl accident,
the Institute is now looking into the health consequences of the Fukushima accident, under a cooperationagreement with the Fukushima Medical University (FMU) in Japan;•exposure of nuclear workers: IRSN has set up a cohort of over 80,000 nuclear workers in France and is participatingin the international INWORKS project. The project includes over 300,000 employees in France, the UK, and the U.S.A.
The results confirm that low doses result in a slight increase in the risk of cancer as well as cardiovascular andcerebrovascular disease. They also highlight the need to strengthen communication on low dose risks and reflection
on “risk acceptability”;•

medical exposure: the Institute has assembled a cohort of over 100,000 children exposed to a first CT scan between
2000 and 2011 in various French university hospitals. Early results suggest an increased risk of brain tumor anddose-associated leukemia in children not predisposed to cancer. However, the short follow-up and the low numberof cancer cases in the cohort do not, as it stands, provide sufficient statistical power to confirm this result. In thisrespect, international partnerships are underway, including under the European EPI-CT and MEDIRAD projects.

In parallel with epidemiological research, IRSN conducts research on the biological effects of low doses, in the field of
human and environmental toxicology. These aim to better understand the biological mechanisms generated byexposure to ionizing radiation, whether in connection with cancer, non-cancer diseases, or on mechanisms oftransgenerational effects (biological modifications in non-exposed offspring of exposed individuals).

IRSN’s contribution to dosimetry monitoring and information on low doses
In France, IRSN publishes periodic radiation monitoring reports on professionals exposed to ionizing radiation, on
patients exposed for medical reasons (ExPRI reports), or on the entire French population (ExPOP reports). It also
publishes fact sheets, such as radon in homes and ways to reduce levels.
Internationally, the Institute is actively involved in the activities of the major radiation protection bodies, such as ICRP,UNSCEAR, the International Atomic Energy Agency (IAEA), and the OECD Nuclear Energy Agency (NEA).